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Dykes, cups, saucers and sills: Analogue experiments on magma intrusion into brittle rocks

Mathieu Lucie, van Wyk de Vries Benjamin, Holohan Eoghan P. et Troll Valentin R.. (2008). Dykes, cups, saucers and sills: Analogue experiments on magma intrusion into brittle rocks. Earth and Planetary Science Letters, 271, (1-4), p. 1-13.

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URL officielle: https://doi.org/10.1016/j.epsl.2008.02.020

Résumé

Magma is transported in the crust by blade-like intrusions such as dykes, sills, saucers, and also collects in thicker laccoliths, lopoliths and plutons. Recently, the importance and great number of shallow (<5 km) saucer-shaped intrusions has been recognized. Lopoliths and cup-shaped intrusions have also been reported in many geological contexts. Our field observations indicate that many intrusions, especially those emplaced into breccias or fractured rocks, have bulging, lobate margins and have shear faults at their bulbous terminations. Such features suggest that magma can propagate along a self-induced shear fault rather than a hydraulic tension-fracture. To investigate this we use analogue models to explore intrusion propagation in a brittle country rock. The models consist of the injection of analogue magma (honey or Golden syrup) in a granular material (sand or sieved ignimbrite) that is a good analogue for brittle or brecciated rocks. These models have the advantage (over other models that use gelatin) to well represent the properties of brittle materials by allowing both shear-faults and tension fractures to be produced at suitable stresses. In our experiments we mainly obtain vertical dykes and inverted-cone like structures that we call cup-shaped intrusions. Dykes bifurcate into cup-shaped intrusions at depths depending on their viscosity. All cup-shaped intrusions uplift a central block. By injecting against a vertical glass plate we obtain detailed observations of the intrusion propagation style. We observe that dykes commonly split and produce cup-shaped intrusions near the surface and that shear zone-related intrusions develop at the dyke tip. We conclude that many dykes propagate as a viscous indenter resulting from shear failure of host rock rather than tensional hydraulic fracturing of host rocks. The shear propagation model provides an explanation for the shape and formation of cup-shaped intrusions, saucer-sills and lopoliths.

Type de document:Article publié dans une revue avec comité d'évaluation
ISSN:0012-821X
Volume:271
Numéro:1-4
Pages:p. 1-13
Version évaluée par les pairs:Oui
Date:2008
Sujets:Sciences naturelles et génie > Sciences naturelles > Sciences de la terre (géologie, géographie)
Département, module, service et unité de recherche:Départements et modules > Département des sciences appliquées > Unité d'enseignement en sciences de la Terre
Mots-clés:dykes, magma, cup-shaped-intrusions, analogue models, viscous indenter, digues, intrusions en forme de coupe, modèles analogues, pénétrateur visqueux
Déposé le:21 oct. 2019 23:53
Dernière modification:21 oct. 2019 23:53
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